CODEWITHSUNDEEP
powershell
Jake
Jake

Reputation: 1781

Variable supposedly not null despite never having a value assigned

Code shortened for brevity:

Function Add-DatabaseUser
{
Param(
    [Parameter(Mandatory=$true, Position = 0)]
    [string] $samaccountname
   ,[Parameter(Position = 1)]
    [string] $username = $null
)

if ($samaccountname -notmatch "[a-z0-9]*\\[a-z0-9]")
{
    throw new [System::ArgumentException] "SAMAccountName was not in the correct format."
}

if($username -eq $null)
{
    $username = $samaccountname
}

# Code omitted...

Try
{
    Write-Host "Creating user..."
    $user = New-Object ("Microsoft.SqlServer.Management.Smo.User") $database, $username
    $user.Login = $login.Name
    $user.Create() # Exception thrown.
}
Catch
{   
    # Code omitted.
}

The exception I get is as follows:

An object or column name is missing or empty. For SELECT INTO statements, verify each column has a name. For other statements, look for empty alias names. Aliases defined as "" or [] are not allowed. Change the alias to a valid name.

This is happening because the value of $username is null. Yet I have a if-statement at the very beginning of the script to check if it it's null, and if so, assign a value to it. But apparently the debugger evaluates $username -eq $null to False.

Why is this?

Edit: Should probably mention this is how I'm calling the function in PowerShell:

Add-DatabaseUser -samaccountname "mycomputer\username"

Upvotes: 3

Views: 570

Answers (1)

omrsafetyo
omrsafetyo

Reputation: 351

I believe this is because you are typecasting the username variable as a string, and then setting it to $null as a default value. The typecasting is causing it to become a null string, or "", which is different than $null.

Get rid of your typecast, or also evaluate :

if( [string]::IsNullOrEmpty($username) )
{
    $username = $samaccountname
}

Edit:

Original answer was the following, but there is a better way:

if($username -eq $null -or $username -eq "" )
{
    $username = $samaccountname
}

Upvotes: 3

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